Instructions here for an older model of Elwood:
http://www.cameraeccentric.com/html/info/elwood_1.html
The newer Elwood listed on eBay has a built-in masking device just above the negative carrier. So if you put for instance a 4X5 negative in the 5X7 glass carrier, you turn knobs to adjust the masks in to block stray light around the neg. Omega D 4X5 enlargers have a similar system as an accessory. There is also a filter drawer above the negative carrier.
The long rectangular box mounted below the diffusion dome in the first picture is somewhat of an oddity. The guy I bought mine from at a camera swap referred to it as a "flip-flop head". If it isn't obvious from the pictures, there are 6 or 7 drawers on either side of the head which hold color printing or variable contrast filters. Depending on what filter strength you want, you slide one or more drawers over into the light path above the negative. The filters needed are larger than the common Ilford 6x6" Multigrade filters, but I believe it is possible to use acetate lighting filters since they are mounted above the negative. I've never mounted my flip-flop head although it seems useful for VC filters. I actually forgot I owned the thing until I saw the eBay pics. It should be easily removable from this enlarger is you don't want to use it.
On my Elwood, I've removed the diffusion dome and made an adapter from 3/4" plywood to set an 8X10 Aristo cold light head for a light source. This places the light a few inches above the negative which I believe isn't supposed to be ideal, but it works. It is always in the back of my mind to cook up an 8X10 negative carrier and mount it up under the cold light head as Rick A suggested. There are articles online on making LED variable contrast light sources which would be a good way to go for anyone with the fabrication skills.
I'm really curious about the pile of negative carrier shown. The lower two in the picture appear to be 5X7 glass carriers like the one I have. The others I'm not sure of. One may be for holding two strips of 120 negs. I'd love to paw through the other carriers and see if I could figure them out.
Len
